Microgravity experiments of flame propagation in ethanol droplet-vapor-air mixture

Abstract

A basic study of spray combustion has been made with a rapid expansion apparatus that can produce monodispersed fuel droplet clouds under microgravity conditions. The effects of droplets on flame propagation were investigated for ethanol droplet-vapor-air mixtures. The pressure of the fuel droplet-vapor-air mixtures was set at 0.2 MPa for all experiments. The total equivalence ratio varied in the range of 0.6–1.6. The ratio of the liquid fuel mass to the total fuel mass varied from 0% to 60%, and the mean droplet diameter ranged from 7 to 45 μm. It was found that the flame speed of fuel droplet-vapor-air mixtures exceeded that of premixed gases of the same total equivalence ratio in two regions of the total equivalence ratio. One region exists on the fuel-lean side, the other exists on the fuel-rich side. For mixtures of 0.3 in the liquid equivalence ratio, the increase in the mean droplet diameter from 7.5 to 11 μm caused an increase in the flame speed in the region where the flame speed increases with the increase in the total equivalence ratio. In contrast, in the region where the flame speed decreases with the increase in the total equivalence ratio, an increase in the mean droplet diameter caused the flame speed to decrease. For mixtures with a mean droplet diameter of 11 μm, an increase in the liquid equivalence ratio from 0.2 to 0.3 caused an increase in the flame speed in the region where the flame speed decreases with the increase in the total equivalence ratio. For mixtures with a total equivalence ratio of 0.8 the flame speed reached its maximum value when the mean droplet diameter was about 11 μm and the liquid equivalence ratio was about 0.2.